To ask about options in cars for kids who won’t stay in booster seats?

If your in the UK contact The InCar Safety Centre. They'll be able to advise you on car seat options that are suitable for your car, your DS height/weight and need for safety. They also sell a buckle cover if he's undoing it, although sounds more like he's not wearing the seatbelt properly so may not work.

There are many children with additional needs, or even adult-sized, who don't understand safety and have to be safely restrained in cars, so yes there are appropriate escape-proof options for larger children.

You'll need to keep using a 5-point harness with an anti-escape cover for as long as is necessary to keep your child safe.

Google for Car Seat SEN

Answering your question, if you think he would tolerate being rear-facing, there are seats like the Axkid Move which will go to 25 kg, which should last you until age 6/7. They have harnesses - they’re not easy seats to move between cars, though. Finding a harnessed forward-facing seat with a weight limit of over 18kg can be challenging.

And in broader terms - some kids are ND but some are just little horrors about certain things…. And it can take time to find out what motivates them enough to get them to comply with something they don’t want to do.

A typically developing NT 4 year old should not still need to be fed and should not be incapable of following a simple safety instruction like "stay in your car seat".

Why are you so sure he isn't ND?

In answer to your actual question, you'll just have to get a bigger 5 point harness seat. There's no other safe option.

My 2 year old is bloody Houdini when it comes to car seats and prams. In the end I got a extra harness, I think it's called an escape-me-not. It works at keeping him in a 5 point harness.

Doesn’t work according to who?
You’ve never had a parenting ‘result’ for telling your child what big children do and they wanting to follow suit? I find that hard to believe.

It sounds incredibly frustrating @Nosnowjustrainandwind!!

If he’s about to outgrow his old seat then personally I would look at replacing it with an extended rear facing seat as it’s the safest way for children of his age to travel.
The recommendation is that they are rear facing in a harness and not forward facing until they can safely sit with a normal seat belt. Forward facing with a harness isn’t the safest option.

My 4yo son is in a Britax Romer Max-Safe Pro. It’s rear facing to 36kg and he’ll easily fit in it until 6/7 👍🏻 They’re on sale at the moment for about £170 if you could stretch to that.

Fingers crossed by the time he’s outgrown the actual car seat he’ll also have outgrown getting out of it…and if not, he’ll be a bit older and can face the consequences

My parents did that to me. My older siblings taught me how to undo the clip on my car seat at about 3 years old. I vaguely remember it still and it was very effective!

I’m sorry @Nosnowjustrainandwind but you have been unreasonable this entire thread.

You can’t buy your way out of every problem with your son, and find a product to work around every behaviour issue.

He is 4.

That means he still believes you hung the moon in the sky. You are the beginning and end of the law.

So If he can’t sit in his seat? That is a parenting problem. NOT a device or manufacture problem.

…unless of course this whole thread is a drip feed and you’re about to tell us he has undiagnosed ADHD, or ASD. etc…for which I have my understanding, but… he’ll still need clear rules and a suitable car seat!

As this hasn’t featured so far, I’m afraid this is a discipline and parenting thing.

One thing that fascinates me -

You describe your son’s attitude to being told off as “he doesn’t care” about ten times in this thread.

Do you think that’s it now? He didn’t respond well a few times, so that’s it now at the age of 4? He is “who he is” and it will never change?

Look for a group 2/3 seat with a 5 point harness; when my DD grew out of the Maxi Cosi Pearl we got the Kindercraft SafetyFix. It has a 5 point harness that fit her until she was 6, at which point you can use it with the seatbelt.

Disagree. Toileting and bike riding are both examples of situations where children need to learn a skill at their own pace and should absolutely have nothing other than encouragement and praise for.
Being wilfully naughty isn’t the same.

I have a Joie Elevate for my granddaughter. She's now five and I still use the harness (though there's the option to just use the seatbelt). There's still a load of room to adjust the harness should I continue with it for another year or so.

Sure just ignore the behaviour..... that always end well!

Well, as previously, I don’t see how OP will get him in a 5 point harness seat if he won’t even sit in a booster seat. I was trying to think of language that would bother 4 year olds (or at least any 4 year old I’ve ever met).

The mocking "oh you're not a big boy look in your baby seat" is what's got my back up.
If your children were still RF (amazing btw) then you should surely see how this is very poor advice. Her child doesn't need mocking for not sitting like a "big boy", he needs a seat suitable for his measurements, age and maturity level.

@Nosnowjustrainandwind so you never ever have any time off work? Not ever?

Might as well carry on having him be unsafe in the car then clearly as you arent keen on any suggestions or solutions. Crack on.

My kids were too tall for the strap height of their 5-point harness seats well before they hit the weight limit. Sadly, most car seat manufacturers don’t provide this information easily so it’s hard to compare.